In order to control weeds in your Oklahoma lawn, apply pre-emergent twice per year—once in spring and once in fall. The timing for these applications is:
- Spring: February 1–March 15
- Fall: August 15–September 15
You will get the best results from your pre-emergent application by further pinpointing timing based on soil temperature, but these date ranges are good working guidelines for Oklahoma.
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Why Pre-Emergent Timing is Important in Oklahoma
Pre-emergent herbicides provide the biggest benefit when they are timed optimally. They work by entering the soil and remaining there for up to 6 weeks. During this time, they kill any seed that germinates underground.
Pre-emergent won’t kill dormant seeds or weeds that have already come up. If you apply too early, you’ll waste your pre-emergent on soil full of dormant seeds. If you apply too late, the weeds will have already broken the soil’s surface and pre-emergent won’t kill them.
- Pre-emergent only kills seeds as they actively germinate (sprout) underground.
- Pre-emergent does not kill dormant seeds or weeds that have already established themselves.
- After application, pre-emergent is active for 6 weeks.
- To maximize effectiveness, time pre-emergent application just before weed seeds begin to germinate.
When timed correctly, pre-emergent stops broadleaf weeds and grassy weeds in their tracks. It’s a very powerful tool to stop the annual weeds that plague Oklahoma yards.
Spring Pre-Emergent Timing for Oklahoma
Although the date range of early February through mid-March is a good ballpark for applying spring pre-emergent throughout Oklahoma, the best way to pinpoint your pre-emergent timing is by monitoring soil temperature and applying accordingly. Here’s how:
- Typical application timing is from February 1 through March 15.
- Spring weeds begin to germinate as soil temperatures (not air temperatures) climb toward 55℉.
- Monitor soil temperatures in your region with this free online soil temperature map.
- Once soil temperatures have risen to 55℉ for 2–3 consecutive days, it’s time to spread pre-emergent.
- This will ensure 100% of your pre-emergent’s 6-week lifespan is used to combat spring and summer annual weeds.
As a rule of thumb, soil temperatures are usually 10 degrees cooler than daytime air temperatures. This calculation is less accurate than a soil temperature map, but can be used in a pinch.
Fall Pre-Emergent Timing for Oklahoma
Annual bluegrass is a wintertime blight on many Oklahoma yards, but it’s not alone. Henbit and common chickweed are also habitual fall invaders. A second application of pre-emergent herbicides will stop these annual weeds.
- Average application timing between August 15 and September 15
- Winter annuals begin to germinate as soil temperatures fall toward 70℉ at the end of summer.
- Optimal fall pre-emergent timing is when soil temperatures dip down to 70℉ for 2–3 consecutive days.
Whatever type of weed or invasive grass you’re up against, a well-timed pre-emergent application in fall will keep your lawn weed free through fall and winter.
What is the Best Pre-Emergent Herbicide for Oklahoma Lawns?
In Oklahoma, most lawns are planted with warm-season grasses. Therefore, it’s essential to choose a pre-emergent that is optimized for warm-season grasses and the weeds that grow in the region. Barricade and Prodiamine WDG are two of the best choices for lawn care in Oklahoma.
- Choose a pre-emergent formulated for warm-season lawns.
- Avoid products that contain Atrazine unless your lawn is St. Augustine, Centipede, or Zoysia grass. Atrazine will harm other turfgrass types, like Bermuda grass.
- Apply pre-emergent according to product label rates.
In order to maximize pre-emergent effectiveness, follow manufacturer instructions for application rates. Do not overapply pre-emergent. Herbicides applied at excessive levels can harm turf grasses.
Should You Mow Before Applying Pre-Emergent?
Pre-emergent needs to make contact with soil so it can be absorbed once you water it in. Mowing your lawn to 1.5–2 inches in height before applying pre-emergent allows more of the herbicide to reach the soil and yields better results stopping broadleaf weeds and grassy weeds.
- Mow grass lower than normal (1.5–2 inches) prior to spreading pre-emergent.
- Check your lawn’s thatch layer. If it’s thicker than 0.5 inches, dethatch to allow pre-emergent to reach soil.
- The more easily pre-emergent reaches the soil, the more effective it will be.
Thick thatch works as a barricade that prevents pre-emergent herbicides from reaching the ground. Dig up a small section of your yard and measure the thatch layer. If it’s more than 0.5 inches thick, it’s time to dethatch. Mowing and dethatching will make your pre-emergent application far more effective.
Do You Need to Water in Pre-Emergent?
Watering in pre-emergent is essential to putting it to work in your yard. If your pre-emergent comes in granule form, it must be watered in to dissolve it and allow it to break down.
- Most pre-emergent is delivered in granule form. Watering dissolves it and allows it to penetrate soil.
- After application, water pre-emergent into soil with 0.5 inches of water (about 30–60 minutes with a sprinkler).
If you are using a liquid pre-emergent or granules that you dissolve in water before application (such as Prodiamine WDG) then you may not need to water following application. Review product label guidelines.
How Long Does it Take for Pre-Emergent to Work?
Once your pre-emergent has been applied and watered in, it will begin to work. Remember, with pre-emergent the best results will be invisible. Under the surface of your Oklahoma lawn, the pre-emergent will attack seeds as they attempt to sprout. If you’re not seeing new weeds, the pre-emergent is working.
- Pre-emergent begins working immediately after being watered into soil.
- Pre-emergent will kill germinating seeds below ground for approximately 6 weeks.
A correctly timed and applied pre-emergent will stop broadleaf weeds, annual bluegrass, and grassy weeds for 6 weeks. A spring application will stop summer weeds, and a fall application will make sure winter annuals don’t sprout.
What is the Best Time to Apply Pre-Emergent in Oklahoma?
To stop summer annual weeds, apply pre-emergent to your Oklahoma yard in early spring, between February 1 and March 15, once soil temperatures rise to 55℉.
To halt winter annual weeds, plan your pre-emergent herbicide application between August 15 and September 15, when soil temperatures fall to 70℉.
These two applications will stop all types of weeds, from invasive spring weeds, to ugly winter weeds. The result of using a few well-timed herbicides is a beautiful Oklahoma lawn free of grassy and broadleaf weeds.